Background
Tachycardia is a physiological mechanism for adapting cardiac output to modifications in energy consumption in the organism. The repercussions that short-duration tachycardia has on myocardial contractility have not been sufficiently studied.
To study the effects of short-duration tachycardia on regional myocardial function in the anterior face of the left ventricle depending on the rate, duration, and origin of the electrical stimulation producing the tachycardia.
Material and Method
Two series were studied in an in vivo canine experimental model. Stimulation was performed in the right atrium and in the base of the left ventricle at a frequency 20 and 40% above the basal rate. The duration of each pacing episode was 10, 20, and 40 minutes followed by a recovery period of 40 minutes. ECG, left ventricular pressure, and regional function curves of a myocardial segment were studied.
Results
During atrial pacing there was a similar decrease in both regional segment lengths (end-systolic and end-diastolic lengths) and no variation in the shortening fraction or in hemodynamic parameters. During ventricular pacing, systolic pressure in the left ventricle decreased, end-diastolic pressure increased, end-diastolic length shortened (meaning less ventricular filling), and the end-systolic length increased, leading to a reduced shortening fraction or regional contractility alteration which was temporarily maintained once pacing ceased.
Conclusions
The transient persistence of segment dysfunction after induced ventricular tachycardia ceases indicates the activation of a different, unknown mechanism.

Keywords: Ventricular Function, Left - physiology, Myocardial Contraction - physiology, Tachycardia, Ventricular - physiopathology, Electric Stimulation, Dogs, Time Factors, Cardiac Output